1. Field of the Invention
The invention relates to a method of fabricating a copper capping layer, and more particularly to a method of fabricating a copper capping layer, thereby improving adhesion between copper and dielectrics.
2. Description of the Related Art
Due to their high degree of conductivity, aluminum and aluminum alloy have been important as conductive materials in the development of the integrated circuit (IC). However, integration of semiconductors has rapidly increased, and the conductivity of aluminum and aluminum alloy can no longer satisfy the speed requirements for semiconductor devices. Therefore, copper is gradually replacing aluminum as a conductive material, because of copper""s lower resistance. In additional, copper is more resistant than aluminum to electromigration, and therefore, the trend in the semiconductor industry is to use copper as a conductive material.
Although copper has the advantages as described above, copper still readily diffuses into dielectrics, and diffuses especially easily into silicon dioxide. Diffusion of copper into dielectrics causes electrical shorts; it is therefore necessary to form a barrier layer between copper and dielectrics. In the conventional process, a tantalum/tantalum nitride layer is usually formed on the bottom and sidewalls of the copper interconnect in order to prevent copper from diffusing into the surrounding silicon dioxide. A silicon nitride layer is typically used to cap the copper interconnect. The silicon nitride layer functions as a protective layer for the silicon dioxide layer formed in subsequent processes and reduces probabilities that copper might diffuse into the dielectrics. However, the silicon nitride layer adheres poorly to copper, which causes the silicon nitride to easily peel away from the copper, creating a path for copper to diffuse outward and for moisture or other contaminates to diffuse inward.
Therefore, the invention is directed towards a method of fabricating a copper capping layer. A silicon rich nitride (SRN) layer is formed on a copper layer, which is exposed. Since there are more dangling bonds in the SRN layer, the silicon in the dangling bonds inside the SRN layer react with the copper layer to form a copper silicide between the SRN layer and the copper layer. Adhesion between the SRN layer and copper is enhanced and, therefore, peeling of the SRN layer from the copper layer is avoided, thereby increasing reliability of devices.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.